This invention relates to apparatus and procedures for carrying out fouling tests in a laboratory environment. More particularly, the fouling test involved is one designed to simulate a heat exchanger surface such as a particular section of a heated exchanger tube exposed to a fouling liquid medium.
In designing apparatus and procedures of the type involved, the problem is to generate and measure in a laboratory environment a fouling deposit representative of that produced in the field. The information obtained by carrying out such fouling tests enables various antifoulant treatments to be evaluated as well as other factors which may mediate the fouling process.
The prior art has addressed the problem in a number of different ways, using types of apparatus and procedures which may be summarized as follows:
1. Pipe loops--These mainly involve procedures wherein very large quantities of oil are pumped through a heated pipe section of some sort and the foulant deposited on the pipe surface (either inner or outer, depending on which surface is heated) during the test is weighed. In addition to requiring large quantities of oil, very complex and expensive equipment, e.g. flowmeters, flow controller and pumps, is required. Moreover, because fouling severity depends upon the heat transfer coefficient, which is influenced by the flow and flow changes along the length of the pipe, the fouling is ill-defined and poorly reproduced. 2. Pilot scale heat exchangers--These involve procedures where, employing pilot scale heat exchangers, heat transfer coefficients are utilized as a measure of fouling. These suffer from the same disadvantages as pipe loops and, in addition, require very long times to establish a fouling condition. Moreover, the fouling cannot be quantified by measurement, since the heat transfer coefficient measures the net effect of all the tubes, which may be in varying conditions of cleanliness.
3. Autoclaves--These include autoclaves provided with either rotating heated cylinders or with stationary heated cylinders under stirred or flow through situations. The use of rotating heating cylinders is an effective way to generate fouling at well defined flow conditions, but requires expensive and hard to maintain rotating electrical feed throughs. Such rotating feed throughs may become hazardous when gaseous petroleum environments are involved. Stationary heated cylinders in stirred or flow through autoclaves are not capable of establishing a well defined and reproducible flow field.
4. Hot wire elements--In this procedure, a preheated oil stream contacts a hot metal wire, the temperature of the wire modeling a heat exchanger's hot wall temperature. However, in this procedure, the velocity effects on the deposit growth are not reproducible.
5. Filtration devices--In these procedures, oil is pumped through heated filters. Deposits build up, plugging the filters. However, there is no way to simulate the velocity effect in these procedures.
An object of the present invention is to provide a fouling test apparatus producing a well defined and reproducible flow field. A further object of the invention is to provide such apparatus having no rotating electrical feed-throughs. An additional object of the invention is to provide such apparatus wherein a signal representing fouling severity can be directly related to an actual physical measure of fouling, such as foulant thickness or weight. Yet another object of the invention is to provide such apparatus wherein small amounts of test fluid are required, in situ fouling monitoring is possible, a short time is required for determining fouling tendency, and specific fouling conditions may be maintained for long periods of time, thereby allowing detailed studies of these conditions. Other objects of the invention, including the provision of procedures for employing such apparatus, will become apparent from the following description and the appended drawing.